There is all kinda of data that I wish were made available through some API, such as the congressional voting data that I mentioned previously. There are lots of businesses and organizations that have data, but not necessarily the resources to create an API.
This is another great use of RSSBus. You can create RSSBus scripts that can take advantage of things like SqlOps and OracleOps, ExcelOps, CcOps, QbOps, FileOps, S3Ops, etc. Through these scripts you can expose an API for your data that is stored in these sources very simply. One example of this is how I effectively created a new API call for Upcoming.org, which I just recently made live here at textbox1.com.
Update: I discovered, and repaired, a bug in FeedMapping my new feed caused by my mishandling of html entities.